The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by plastic wall panels that is vented via thinned wall sections that rupture in response to inflation pressures.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions made of various fabrics that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2, 2013, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or trim panel that faces a vehicle occupant attached to a back wall or bladder wall along a sealed periphery. One or both of the walls is deformable in order to provide an expandable, inflatable bladder. For example, the bladder wall may have a pleated (i.e., accordion-like) region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The front and back walls of a typical bladder for an active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but can also be blow molded. When formed separately, the front and back walls must be hermetically joined around their periphery in order to ii) form the inflatable bladder. The joint must be strong to resist separation that could result from high inflation pressures during inflation and that result when a passenger impacts the bolster. The peripheral seal is formed by hot welding, for example.
It is known that in order to optimize the dissipation of energy when an occupant contacts an air bag or an active bolster, inflation gas should be vented to allow a controlled collapse of the airbag that safely decelerates the impacting occupant. U.S. Pat. No. 8,328,233, issued Dec. 11, 2012, which is incorporated herein by reference, discloses a variable vent for an active bolster wherein the vent has a low flow rate at low pressures and a higher flow rate at higher pressures across the vent. The reduced flow rate of the vent during initial stages of inflation permits the use of a smaller (less costly) inflator, while the higher vent flow rate at higher pressures helps ensure the integrity of the peripheral weld by limiting the pressure rise and avoiding large tearing forces that could cause the seal to fail.
Various types of structures and locations have been disclosed for adaptively venting inflation gas during inflation and during loading by an impacting passenger. Venting locations have been disclosed on the central, flat areas of the bladder wall facing the front wall, in upstanding ribs on the front, trim wall that form a peripheral weld track, and in the pleated baffle region of the bladder wall, for example. Previously disclosed structures for forming active vents have been relatively complex and have required complicated manufacturing steps that result in increased manufacturing costs. Known vents have also been typically placed on structures that may significantly deform during bladder inflation, which results in changes in the venting during deployment that are difficult to control or predict. Furthermore, known areas for vent placement are not always large enough to accommodate all the required venting area.